Chamaecrista nictitans aka Sensitive Pea

Chamaecrista nictitans, or sensitive pea, belongs to the pea family. Its native range spans the central and eastern United States south through tropical America. It reaches Argentina and also occurs in the Caribbean. It grows in prairies, open woods, thickets, and disturbed ground. It also lives along both wet and dry shores. Most plants live for one year and reseed themselves. Some persist as short-lived perennials with a woody base.

Garden plants reach about 0.3–1.7 feet [0.1–0.5 metres] tall. Other accounts give heights up to 3.3 feet [1 metre]. Several upright, green stems give the plant a fine texture. The round stems are smooth or bear very short hairs. Alternate, compound leaves hold 20–36 small leaflets. Each leaflet has smooth edges and a tiny spine tip. Touch or disturbance can cause the leaflets to fold together. This response gives sensitive pea its common name.

Small yellow flowers open from June through September. They grow where the leaves join the stems. Flowers appear alone or in groups of two or three. Each pea-shaped flower has unequal petals but matching sides. The lower petals are twice the length of the others. Flat, oblong legumes follow the flowers in summer and fall. These brown pods reach about one to three inches long. Ripe pods split along their seams, exposing smooth brown or black seeds.

Full sun gives better growth, though plants tolerate some shade. They grow in sand, loam, and clay with good drainage. Sandy soil suits them well. Poor drainage can cause the long taproot to rot. Plants tolerate soil that dries or becomes wet at times. They grow fast and need little routine care. Sow seeds in late spring or early summer. Place them a quarter to three-quarters of an inch deep. Seeds sprout quickly, and plants can spread into nearby disturbed ground.

Sensitive pea adds nitrogen to soil and serves as a cover crop. Its deep root helps hold soil on banks and slopes. It suits meadows, woodland edges, and gardens for native plants. Bees visit the flowers, and birds and small mammals eat seeds. Little sulphur and cloudless sulphur caterpillars use it as a host. Nematodes can damage plants. Some Pacific islands classify it as invasive. Useful Tropical Plants reports no known food uses or hazards. That report does not establish that eating it is safe. Records describe medicinal use, including Cherokee treatments, rather than proven remedies.